Commercial scale microwave heating system

ABSTRACT

A microwave heating system for continuously heating a plurality of articles and process for using the same are provided. The microwave system includes a thermalization zone for thermalizing the articles to a substantially uniform temperature, a microwave heating zone for increasing the temperature of the articles by at least about 50° C., and a quench zone for cooling the articles after heating. The heating can be carried out at a rate of at least 25° C. per minute. The system also includes at least one conveyance system for transporting the articles through each of the thermalization, microwave heating, and quench zones. The system can be commercial-sized and may have an overall production rate of at least 20 packages per minute per convey line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNos. 61/610,708; 61/610,729; 61/610,739; 61/610,745; 61/610,756;61/610,767; 61/610,776; 61/610,787; 61/610,794; 61/610,804; 61/610,821;61/610,830, all filed on Mar. 14, 2012, the disclosures of which areincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to microwave systems for heating one or moreobjects, articles, and/or loads.

BACKGROUND

Electromagnetic radiation, such as microwave radiation, is a knownmechanism for delivering energy to an object. The ability ofelectromagnetic radiation to penetrate and heat an object in a rapid andeffective manner has proven advantageous in many chemical and industrialprocesses. Because of its ability to quickly and thoroughly heat anarticle, microwave energy has been employed in heating processes whereinthe rapid achievement of a prescribed minimum temperature is desired,such as, for example, pasteurization and/or sterilization processes.Further, because microwave energy is generally non-invasive, microwaveheating may be particularly useful for heating ‘sensitive’ dielectricmaterials, such as food and pharmaceuticals. However, to date, thecomplexities and nuances of safely and effectively applying microwaveenergy, especially on a commercial scale, have severely limited itsapplication in several types of industrial processes.

Thus, a need exists for an efficient, consistent, and cost effectiveindustrial-scale microwave heating system suitable for use in a widevariety of processes and applications.

SUMMARY

One embodiment of the present invention concerns a continuous processfor heating a plurality of articles in a microwave heating systemcomprising the steps of (a) thermalizing the articles in athermalization zone to thereby provide a plurality of thermalizedarticles having a substantially uniform temperature; (b) heating thethermalized articles in a microwave heating zone to thereby increase theaverage temperature of each article by at least 50° C., wherein at leasta portion of the heating is carried out at a heating rate of at least25° C. per minute; and (c) cooling the heated articles in a quench zone.The articles are passed through each of the thermalization zone, themicrowave heating zone, and the quench zone via one or more conveyancesystems, wherein the microwave heating system has an overall productionrate of at least 20 packages per minute per convey line.

Another embodiment of the present invention concerns a microwave systemfor heating a plurality of articles. The system comprises athermalization chamber for thermalizing the articles to a substantiallyuniform temperature, a microwave heating chamber disposed downstream ofthe thermalization chamber for heating the thermalized articles, and aquench chamber disposed downstream of the microwave heating chamber forcooling the heated articles to a lower temperature. The microwaveheating chamber is configured to increase the average temperature of thearticles by at least 50° C. at a heating rate of at least 25° C. perminute. The system comprises at least one convey system configured totransport the articles through the thermalization chamber, the microwaveheating chamber, and the quench chamber. The microwave system isconfigured to achieve an overall production rate of at least 20 packagesper minute per convey line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is process flow diagram depicting one embodiment of a microwaveheating system for heating one or more articles, particularlyillustrating a system comprising a thermalization zone, a microwaveheating zone, an optional holding zone, a quench zone, and a pair ofpressure adjustment zones;

FIG. 1b is a schematic diagram of a microwave heating system 10configured according to one embodiment of the present invention,particularly each of the zones of microwave heating system 10 outlinedin the diagram provided in FIG. 1 a;

FIG. 2a is a cross-sectional schematic end view of a process vesselconfigured according to one embodiment of the present invention,particularly illustrating a conveyance system including a pair of conveylines arranged in a side-by-side configuration;

FIG. 2b is a schematic top cut-away view of the process vessel shown inFIG. 2a , particularly illustrating the laterally-spaced arrangement ofthe convey lines relative to the convey axis extending through thevessel;

FIG. 2c is a cross-sectional schematic end view of another processvessel configured according to another embodiment of the presentinvention, particularly illustrating a conveyance system including apair of convey lines arranged in a stacked configuration;

FIG. 2d is a schematic side cut-away view of the process vessel shown inFIG. 2c , particularly illustrating the vertically-spaced arrangement ofthe convey lines relative to convey axis extending through the vessel;

FIG. 3 is a perspective view of a carrier according to one embodiment ofthe present invention configured to secure and transport the articlesbeing heated through a liquid-filled process vessel;

FIG. 4a is a partial side cut-away view of one embodiment of a microwaveheating system that includes a pressure adjustment zone configured totransport one or more articles from the thermalization zone to themicrowave heating zone of the heating system using a carrier transfersystem;

FIG. 4b is a partial side cut-away view of another embodiment of amicrowave heating system including a pressure adjustment zone similar tothe one depicted in FIG. 4a , but particularly illustrating a carriertransfer system disposed nearly entirely within the pressure adjustmentzone;

FIG. 4c is a partial schematic view of the pressure adjustment zonesimilar to the ones depicted in FIGS. 4a and 4b , but illustratinganother embodiment of the carrier transfer system for moving thearticles from the thermalization zone to the microwave heating zone;

FIG. 4d is a partial schematic view of the pressure adjustment zonesimilar to the ones depicted in FIGS. 4a and 4b , but illustrating yetanother embodiment of the carrier transfer system for moving thearticles from the thermalization zone to the microwave heating zone;

FIG. 5a is a partial side cut-away view of a locking gate deviceconfigured according to one embodiment of the present invention,particularly showing the gate assembly in an open position;

FIG. 5b is a partial side cut-away view of the locking gate devicedepicted in FIG. 5a , particularly showing the gate assembly in a closedposition with the sealing plates in a retracted position;

FIG. 5c is a partial side cut-away view of the locking gate devicedepicted in FIGS. 5a and 5b , particularly showing the gate assembly ina closed position with the sealing plates in an extended position;

FIG. 5d is an enlarged partial view of the gate assembly shown in FIGS.5a-c , particularly illustrating one embodiment of a bearing used tomove the sealing plates of the gate assembly;

FIG. 6a is a schematic partial side cut-away view of a microwave heatingzone configured according to one embodiment of the present invention,particularly illustrating the heating vessel and the microwavedistribution system;

FIG. 6b is a schematic top view of a microwave heating zone configuredaccording to one embodiment of the present invention, particularlyillustrating one configuration of microwave launchers in a heatingsystem employing a multi-line convey system;

FIG. 6c is a schematic side view of the microwave heating zoneillustrated in FIG. 6b , particularly showing the one set of microwavelaunchers configured to heat articles passing along a convey line;

FIG. 7a is a partial side cut-away view of a microwave heating zoneconfigured according to one embodiment of the present invention,particularly illustrating a titled microwave launcher and showing whatis meant by the term “launch tilt angle” (β);

FIG. 7b is a partial side cut-away view of another embodiment of amicrowave heating zone, particularly illustrating a microwavedistribution system comprising a plurality of tilted launchers;

FIG. 8a is a partial enlarged side cut-away view of a portion of amicrowave heating zone, particularly illustrating one embodiment of amicrowave window located near the discharge opening of at least onemicrowave launcher of the heating zone;

FIG. 8b is a partial enlarged side cut-away view of a portion of amicrowave heating zone, particularly illustrating another embodiment ofa microwave window located near the discharge opening of at least onemicrowave launcher of the heating zone;

FIG. 8c is a partial enlarged side cut-away view of a portion of amicrowave heating zone, particularly illustrating yet another embodimentof a microwave window located near the discharge opening of at least onemicrowave launcher of the heating zone;

FIG. 9a is an isometric view of a microwave launcher configuredaccording to one embodiment of the present invention;

FIG. 9b is a longitudinal side view of the microwave launcher depictedin FIG. 9 a;

FIG. 9c is an end view of the microwave launcher depicted in FIGS. 9aand 9b , particularly illustrating a launcher having a flared outlet;

FIG. 9d is an end view of another embodiment of the microwave launchergenerally depicted in FIGS. 9a and 9b , particularly illustrating alauncher having an inlet and outlet of approximately the same size;

FIG. 9e is an end view of yet another embodiment of the microwavelaunchers generally depicted in FIGS. 9a and 9b , particularlyillustrating a launcher having a tapered outlet;

FIG. 10a is an isometric view of another microwave launcher configuredaccording to one embodiment of the present invention, particularlyillustrating a launcher comprising a single microwave inlet and aplurality of microwave outlets;

FIG. 10b is a vertical cross-sectional view of the microwave launcherdepicted in FIG. 10a , particularly illustrating the multiple microwaveoutlets;

FIG. 10c is a vertical cross-sectional view of the microwave launcherdepicted in FIGS. 10a and 10b , particularly showing the pair ofdividing septa used to create individual microwave pathways between theinlet and multiple outlets of the microwave launcher;

FIG. 11a is an isometric view of a microwave launcher configuredaccording to yet another embodiment of the present invention,particularly showing an integrated inductive iris disposed between theinlet and outlet of the launcher;

FIG. 11b is a horizontal cross-sectional view of the microwave launcherdepicted in FIG. 11 a;

FIG. 11c is a horizontal cross-sectional view of another microwavelauncher similar to the launcher depicted in FIG. 11a , but including apair of dividing septa in addition to an inductive iris disposed betweenthe inlet and outlet of the launcher;

FIG. 12a is a side cut-away view of a phase shifting device configuredaccording to one embodiment of the present invention, particularlyillustrating a plunger-type tuning device that includes a singleplunger;

FIG. 12b is a schematic side cut-away view of a phase shifting deviceconfigured according to another embodiment of the present invention,particularly illustrating a plunger-type tuning device including aplurality of plungers driven by a common rotatable shaft;

FIG. 13a is a side perspective view of a phase shifting deviceconfigured according to yet another embodiment of the present invention,particularly illustrating a rotatable phase shifting device;

FIG. 13b is a longitudinal cross-sectional view of the rotatable phaseshifting device depicted in FIG. 13 a;

FIG. 13c is a lateral cross-sectional view of the rotatable section ofthe rotatable phase shifting device depicted in FIGS. 13a and 13b ,particularly showing the width and spacing of the plates disposed withinthe housing;

FIG. 13d is an lateral cross-sectional view of the fixed section of therotatable phase shifting device depicted in FIGS. 13a and 13b ,particularly illustrating the dimensions of the fixed section;

FIG. 13e is a side cut-away view of a rotatable phase shifting deviceconfigured according to another embodiment of the present invention,particularly illustrating a drive system that includes a rotating crankmember;

FIG. 13f is a side cut-away view of a rotatable phase shifting deviceconfigured according to yet another embodiment of the present invention,particularly illustrating a drive system that includes a set ofcompression springs;

FIG. 14a is a schematic partial side cut-away view of a microwavedistribution system utilizing two phase shifting devices for phaseshifting and/or impedance tuning;

FIG. 14b is a schematic partial side cut-away view of a microwaveheating vessel configured according to one embodiment of the presentinvention, particularly illustrating a phase shifting device coupled tothe vessel for use as a frequency tuner;

FIG. 15a is a schematic partial side cut-away view of a portion of amicrowave heating system, particularly illustrating a thermalizationzone including a plurality of fluid jet agitators;

FIG. 15b is an end view of a thermalization zone similar to the onedepicted in FIG. 15a , particularly illustrating one embodiment whereinthe fluid jet agitator is circumferentially-positioned within thethermalization zone;

FIG. 16 is a flowchart representing the major steps involved in a methodof controlling a microwave system in accordance with one embodiment ofthe present invention;

FIG. 17 is a flowchart representing the major steps involved in a methodfor determining the net power discharged from at least one microwavelauncher using two or more pairs of directional couplers; and

FIG. 18 is an isometric depiction of the location of thermocouplesinserted into a test package to determine the minimum temperature of thepackage for determining the heating profile for an article according toone embodiment of the present invention.

DETAILED DESCRIPTION

Microwave processes and systems for heating a plurality of articlesaccording to various embodiments of the present invention are describedbelow. Examples of suitable articles to be heated in systems andprocesses of the present invention can include, but are not limited to,foodstuffs, medical fluids, and medical instruments. In one embodiment,microwave systems described herein can be used for the pasteurizationand/or sterilization of the articles being heated. In general,pasteurization involves rapid heating of an article or articles to aminimum temperature between 80° C. and 100° C., while sterilizationinvolves heating one or more articles to a minimum temperature between100° C. to 140° C. However, in one embodiment, pasteurization andsterilization may take place simultaneously or nearly simultaneously andmany processes and systems can be configured to both pasteurize andsterilize one or more articles. Various embodiments of microwave systemsand processes configured to heat one or more types of articles will nowbe discussed in detail, with reference to the Figures.

Turning now to FIGS. 1a and 1b , a schematic representation of the majorsteps in a microwave heating process according to one embodiment of thepresent invention is depicted in FIG. 1a , while FIG. 1b depicts oneembodiment of a microwave system 10 operable to heat a plurality ofarticles according to the process outlined in FIG. 1a . As shown inFIGS. 1a and 1b , one or more articles can initially be introduced intoa thermalization zone 12, wherein the articles can be thermalized to asubstantially uniform temperature. Once thermalized, the articles canthen be optionally passed through a pressure adjustment zone 14 a beforebeing introduced into a microwave heating zone 16. In microwave heatingzone 16, the articles can be rapidly heated using microwave energydischarged into at least a portion of the heating zone by one or moremicrowave launchers, generally illustrated as launchers 18 in FIG. 1b .The heated articles can then optionally be passed through a holding zone20, wherein the articles can be maintained at a constant temperature fora specified amount of time. Subsequently, the articles can then bepassed to a quench zone 22, wherein the temperature of the articles canbe quickly reduced to a suitable handling temperature. Thereafter, thecooled articles can optionally be passed through a second pressureadjustment zone 14 b before being removed from system 10 and furtherutilized.

Microwave system 10 can be configured to heat many different types ofarticles. In one embodiment, the articles heated in microwave system 10can comprise foodstuffs, such as, for example, fruits, vegetables,meats, pastas, pre-made meals, and even beverages. In other embodiments,the articles heated in microwave system 10 can comprise packaged medicalfluids or medical and/or dental instruments. The articles processedwithin microwave heating system 10 can be of any suitable size andshape. In one embodiment, each article can have a length (longestdimension) of at least about 2 inches, at least about 4 inches, at leastabout 6 inches and/or not more than about 18 inches, not more than about12 inches, or not more than about 10 inches; a width (second longestdimension) of at least about 1 inch, at least about 2 inches, at leastabout 4 inches and/or not more than about 12 inches, not more than about10 inches, or not more than about 8 inches; and/or a depth (shortestdimension) of at least about 0.5 inches, at least about 1 inch, at leastabout 2 inches and/or not more than about 8 inches, not more than about6 inches, or not more than about 4 inches. The articles can compriseindividual items or packages having a generally rectangular orprism-like shape or can comprise a continuous web of connected items orpackages passed through microwave system 10. The items or packages maybe constructed of any material, including plastics, cellulosics, andother microwave-transparent materials, and can be passed throughmicrowave system 10 via one or more conveyance systems, embodiments ofwhich will be discussed in detail below.

According to one embodiment of the present invention, each of theabove-described thermalization, microwave heating, holding, and/orquench zones 12, 16, 20, and 22 can be defined within a single vessel,as generally depicted in FIG. 1b , while, in another embodiment, atleast one of the above-described stages can be defined within one ormore separate vessels. According to one embodiment, at least one of theabove-described steps can be carried out in a vessel that is at leastpartially filled with a fluid medium in which the articles beingprocessed can be at least partially submerged. The fluid medium can be agas or a liquid having a dielectric constant greater than the dielectricconstant of air and, in one embodiment, can be a liquid medium having adielectric constant similar to the dielectric constant of the articlesbeing processed. Water (or liquid media comprising water) may beparticularly suitable for systems used to heat edible and/or medicaldevices or articles. In one embodiment, additives, such as, for example,oils, alcohols, glycols, and salts may optionally be added to the liquidmedium to alter or enhance its physical properties (e.g., boiling point)during processing, if needed.

Microwave system 10 can include at least one conveyance system (notshown in FIGS. 1a and 1b ) for transporting the articles through one ormore of the processing zones described above. Examples of suitableconveyance systems can include, but are not limited to, plastic orrubber belt conveyors, chain conveyors, roller conveyors, flexible ormultiflexing conveyors, wire mesh conveyors, bucket conveyors, pneumaticconveyors, screw conveyors, trough or vibrating conveyors, andcombinations thereof. The conveyance system can include any number ofindividual convey lines and can be arranged in any suitable mannerwithin the process vessels. The conveyance system utilized by microwavesystem 10 can be configured in a generally fixed position within thevessel or at least a portion of the system can be adjustable in alateral or vertical direction.

Turning now to FIGS. 2a-2d , embodiments of a process vessel 120 thatincludes a conveyance system 110 disposed therein are provided. In oneembodiment generally depicted in FIGS. 2a and 2b , conveyance system 110includes a pair of laterally spaced, substantially parallel convey lines112, 114 positioned in a generally side-by-side configuration withinvessel 120. As shown in the top, cut-away view of vessel 120 in FIG. 2b, convey lines 112 and 114 may be laterally spaced from each other andmay be positioned on both sides of a convey axis 122, which extendsalong the length of vessel 120 in the direction of conveyance of thearticles passing therethrough. Although shown in FIG. 2a as being atgenerally the same vertical elevation within vessel 120, it should beunderstood that, in one embodiment, convey lines 112, 114 may also bepositioned at different vertical elevations. Additionally, conveyancesystem 110 depicted in FIGS. 2a and 2b may also include multiple pairsof laterally spaced convey lines (embodiment not shown), such that thepairs of laterally spaced convey lines are vertically spaced from eachother along the vertical dimension of vessel 120.

Another embodiment of a conveyance system 110 that includes a pair ofvertically-spaced, substantially parallel convey lines 116, 118positioned in a stacked arrangement within the interior of vessel 120,is shown in FIGS. 2c and 2d . Convey lines 116 and 118 may be configuredabove and below convey axis 122, which may generally extend along thelength of vessel 120, as shown in the cutaway side view of vessel 120provided in FIG. 2d . Additionally, in a similar manner as previouslydescribed, vessel 120 shown in FIGS. 2c and 2d may also include multiplepairs of convey lines, laterally spaced from one another within thevessel. Further, each convey line of the pair may or may not be offsetfrom the other in a lateral direction. In a further embodiment (notshown), vessel 120 may include a single convey line, positioned in themiddle one-third of the internal volume of vessel 120, or positioned ator near the centerline of the vessel. Additional details of conveyancesystems according to several embodiments of the present invention willbe discussed in detail below.

When a conveyance system is used to transport articles through aliquid-filled process vessel, one or more carriers or other securingmechanisms can be used to control the position of the articles duringpassage through the liquid medium. One embodiment of a suitable carrier210 is illustrated in FIG. 3. As shown in FIG. 3, carrier 210 comprisesa lower securing surface 212 a and an upper securing surface 212 bconfigured to secure any suitable number of articles 216 therebetween.In one embodiment, upper and/or lower surfaces 212 b,a can have ameshed, grid, or grated structure, as generally depicted in FIG. 3,while, in another embodiment, one or both surfaces 212 a,b can be asubstantially continuous surface. Carrier 210 can be constructed ofplastic, fiberglass, or any other dielectric material and, in oneembodiment, may be made of one or more microwave-compatible and/ormicrowave-transparent materials. In some embodiments, the material maybe a lossy material. In some embodiments, carrier 210 can comprisesubstantially no metal.

Lower and upper securing surfaces 212 a, 212 b may be attached to oneanother by a securing device, shown as a fastener 219 in FIG. 3, and, asassembled, carrier 210 may be attached or secured to the conveyancesystem (not shown in FIG. 3) according to any suitable attachmentmechanism. In one embodiment, at least one side (or edge) of carrier 210can include one or more attachment mechanisms, such as, for example,upper and lower hooks 218 a, 218 b shown in FIG. 3, for securing carrier210 to a portion (e.g., a bar, a rail, a belt, or a chain) of theconveyance system (not shown). Depending on the thickness and/or weightof articles 216, carrier 210 may only include one of hooks 218 a, 218 bfor securing carrier 210 onto the conveyance system. The conveyancesystem used to transport articles 216 may be configured to transportmultiple carriers along one or more conveyance lines and the carriersmay be arranged in a side-by-side, laterally-spaced configuration and/orin a vertically-spaced, stacked configuration as described previously.When the conveyance system includes a plurality of convey lines, eachconvey line may include a single carrier for holding a plurality ofarticles 216, or each convey line may hold multiple carriers stacked orlaterally spaced from each other.

Referring back to FIGS. 1a and 1b , the articles introduced intomicrowave system 10 are initially introduced into thermalization zone12, wherein the articles are thermalized to achieve a substantiallyuniform temperature. In one embodiment, at least about 85 percent, atleast about 90 percent, at least about 95 percent, at least about 97percent, or at least about 99 percent of all the articles withdrawn fromthermalization zone 12 have a temperature within about 5° C., withinabout 2° C., or within 1° C. of one another. As used herein, the terms“thermalize” and “thermalization” generally refer to a step oftemperature equilibration or equalization. Depending on the initial anddesired temperature of the articles being thermalized, the temperaturecontrol system of thermalization zone 12, illustrated in FIG. 1a as heatexchanger 13, can be a heating and/or cooling system. In one embodiment,the thermalization step can be carried out under ambient temperatureand/or pressure, while, in another embodiment, thermalization can becarried out in a pressurized and/or liquid-filled thermalization vesselat a pressure of not more than about 10 psig, not more than about 5psig, or not more than about 2 psig. Articles undergoing thermalizationcan have an average residence time in thermalization zone 12 of at leastabout 30 seconds, at least about 1 minute, at least about 2 minutes, atleast about 4 minutes and/or not more than about 20 minutes, not morethan about 15 minutes, or not more than about 10 minutes. In oneembodiment, the articles withdrawn from thermalization zone 12 can havea temperature of at least about 20° C., at least about 25° C., at leastabout 30° C., at least about 35° C. and/or not more than about 70° C.,not more than about 65° C., not more than about 60° C., or not more thanabout 55° C.

In one embodiment wherein thermalization zone 12 and microwave heatingzone 16 are operated at substantially different pressures, the articlesremoved from thermalization zone 12 can first be passed through apressure adjustment zone 14 a before entering microwave heating zone 16,as generally depicted in FIGS. 1a and 1b . Pressure adjustment zone 14 acan be any zone or system configured to transition the articles beingheated between an area of lower pressure and an area of higher pressure.In one embodiment, pressure adjustment zone 14 a can be configured totransition the articles between two zones having a pressure differenceof at least about 1 psi, at least about 5 psi, at least about 10 psiand/or not more than about 50 psi, not more than about 45 psi, not morethan about 40 psi, or not more than about 35 psi. In one embodiment,microwave system 10 can include at least two pressure adjustment zones14 a,b to transition the articles from an atmospheric pressurethermalization zone to a heating zone operated at an elevated pressurebefore returning the articles back to atmospheric pressure, as describedin detail below.

One embodiment of a pressure adjustment zone 314 a disposed between athermalization zone 312 and a microwave heating zone 316 of a microwaveheating system 310 is illustrated in FIG. 4a . Pressure adjustment zone314 a is configured to transition a plurality of articles 350, which maybe secured within at least one carrier, from lower-pressurethermalization zone 312 to higher-pressure microwave heating zone 316.Although shown in FIG. 4a as being a single carrier 352 a, it should beunderstood that pressure adjustment zone 314 a may be configured toreceive more than one carriers. In one embodiment, the carriers may bereceived simultaneously, such that pressure adjustment zone 314 acontains multiple carriers at one time. In another embodiment, multiplecarriers may be lined up and ready, for example within thermalizationzone 312, for being transitioned through pressure adjustment zone 314 a,details of which will now be discussed below.

In operation, one or more carriers 352 a can be transitioned fromthermalization zone 312 to microwave heating zone 316 by first openingan equilibration valve 330 and allowing the pressure betweenthermalization zone 312 and pressure adjustment zone 314 a to equalize.Next, a gate device 332 can be opened to allow carrier 352 a to be movedfrom a convey line 340 a disposed within thermalization zone 312 onto aplatform 334 within pressure adjustment zone 314 a, as generally shownby the dashed-line carrier 352 b in FIG. 4 a.

Thereafter, gate device 332 and equilibrium valve 330 can be closed insequence, re-isolating pressure adjustment zone 314 a fromthermalization zone 312. Subsequently, another equilibration valve 336can be opened to allow the pressure between pressure adjustment zone 314a and microwave heating zone 316 to equalize. Once equilibrium isachieved, another gate device 338 can be opened to permit carrier 352 bto be moved onto another conveyance system 340 b disposed withinmicrowave heating zone 316, as generally shown by dashed-line carrier352 c in FIG. 4a . Subsequently, gate device 338 and equalization valve336 may be closed in sequence, re-isolating microwave heating zone 316from pressure adjustment zone 314 a. The process may then be repeated totransport additional carriers from thermalization zone 312 to microwaveheating zone 316 as needed.

According to one embodiment, each of microwave heating zone 316 andthermalization zone 312 can be filled with a non-compressible fluid orliquid, such as, for example, water or solutions including water. Asused herein, the term “filled” denotes a configuration where at least 50percent of the specified volume is filled with the filling medium. The“filling medium” can be a liquid, typically an incompressible liquid,and may be or include, for example, water. In certain embodiments,“filled” volumes can be at least about 75 percent, at least about 90percent, at least about 95 percent, or 100 percent full of the fillingmedium. When thermalization zone 312 and/or microwave heating zone 316are filled with an incompressible fluid, gate devices 332, 338 and/orpressure adjustment zone 314 a may also include two or more one-wayflaps or valves, shown as valves or flaps 342, 344 in FIG. 4a , forpreventing substantial fluid leakage between thermalization zone 312 andmicrowave heating zone 316 when gate devices 332 and 338 are open andcarrier 352 is passed therethrough.

The transportation of carrier 352 from thermalization zone 312 throughpressure adjustment zone 314 a and into microwave heating zone 316 canbe accomplished via one or more automatic article transfer systems,several embodiments of which are illustrated in FIGS. 4b-4d . In someembodiments, automatic transfer system 380 can include one or moretransfer devices, disposed within thermalization zone 312, pressureadjustment zone 314 a, and/or microwave heating zone 316 for movingcarrier 352 into and/or out of pressure adjustment zone 314 a. In oneembodiment shown in FIG. 4b , transfer system 380 includes two geartransfer devices 381, 382 configured to engage teeth 353 disposed alongthe lower edge of carrier 352 and rotate, as indicated by the arrows 392a,b, to pull carrier 352 into out of thermalization zone 312 and/or pushcarrier 352 into microwave heating zone 316. As shown in FIG. 4b , firstand second gear transfer devices 381, 382 remain substantiallystationary (in terms of lateral motion) during the transportation ofcarrier 352 and are nearly entirely, or entirely, disposed withinpressure adjustment zone 314 a.

In contrast, some embodiments of automatic transfer system 380 caninclude one or more transfer devices that are laterally shiftable (i.e.,movable in the direction of transport) during transport of carrier 352into and/or out of pressurize adjustment zone 314 a. As depicted in oneembodiment shown in FIG. 4c , a portion of the automatic transfer system380 may be disposed in thermalization zone 312 and/or microwave heatingzone 316 and can be configured for extension into and retraction out ofpressure adjustment zone 314 a. In the system 380 shown in FIG. 4c , thetransfer devices include a pusher arm 381 configured to push carrier 352into pressure adjustment zone 314 a and a puller arm 382 for pullingcarrier 352 into microwave heating zone 316. Neither pusher arm 381 norpuller arm 382 are disposed within pressure adjustment zone 314 a, butinstead, each is configured to extend into and retract out of pressureadjustment zone 314 a, as generally shown by arrows 394 a,b in FIG. 4 c.

According to another embodiment depicted in FIG. 4d , automatictransport system 380 includes a platform 334 having a movable portion384, which is configured to be extended into and retracted out ofthermalization 312 and/or microwave heating zone 316 to therebytransport carrier 352 into and out of thermalization and microwaveheating zones 312, 316, as generally shown by arrows 396 a and 396 b. Incontrast to the embodiment shown in FIG. 4c , automatic transfer system380 depicted in FIG. 4d is primarily disposed within pressure adjustmentzone 314 a and is configured to extend out of and retract back intopressure adjustment zone 314 a.

Regardless of the specific configuration of the transfer devicesutilized by automatic article transfer system 380, the transfer systemcan be automated, or controlled, by an automatic control system 390, asillustrated in FIGS. 4a and 4b . Although not specifically depicted inthe embodiments illustrated in FIGS. 4c and 4d , it should be understoodthat such control systems 390 may also be employed in these embodiments.Automatic control system 390 can be used to control the motion and/ortiming of at least one of first and second equilibration valves 330,336, first and second gate valves 332, 338, and first and secondtransfer devices 381, 382 of the automatic article transfer system 380.In one embodiment, control system 390 can adjust the position, speed,and/or timing of these devices or elements in order to ensure that thecarriers within the system move in an uninterrupted and consistentmanner.

Turning now to FIGS. 5a-5d , one embodiment of a locking gate device420, suitable for use as gate device 332 and/or 338 in the portion ofmicrowave system 310 depicted in FIGS. 4a and 4b , is provided. Lockinggate valve device 420 is illustrated in FIGS. 5a-d as generallycomprising a pair of spaced apart fixed members 410, 412 that presentopposing sealing surfaces 414 a,b and that define a gate-receiving space416 therebetween. The spaced apart fixed members 410, 412 can eachdefine a flow-through opening 418 a,b, which are circumscribed by one ofsealing surfaces 414 a,b. Each of flow-through openings 418 a,b aresubstantially aligned with one another such that the articles can passthrough the cumulative opening when gate valve device 420 is open.

Locking gate device 420 further comprises a gate assembly 422, which isconfigured to be received within gate-receiving space 416 and isshiftable therein between a closed position (as shown in FIGS. 5b and 5c), wherein gate assembly 422 substantially blocks flow-through openings418 a,b, and an open position (as shown in FIG. 5a ), wherein gateassembly 422 does not substantially block flow-through openings 418 a,b.In one embodiment, gate assembly 422 comprises a pair of spaced apartsealing plates 424, 426 and a drive member 428 disposed between sealingplates 424, 426. When gate assembly 422 is configured in the closedposition, drive member 428 is shiftable, relative to sealing plates 424,426, between a retracted position (as shown in FIG. 5b ) and an extendedposition (as shown in FIG. 5c ). In one embodiment shown in FIGS. 5a-c ,gate assembly 422 comprises at least one pair of bearings 430 disposedwithin the space defined between opposing sealing plates 424, 426, whichis positioned in gate receiving space 416 when gate assembly 422 is in aclosed position, as particularly shown in FIGS. 5b and 5c . When drivemember 428 is shifted between a retracted position as illustrated inFIG. 5b to an extended position as depicted in FIG. 5c , at least onebearing of pair 430 can force at least one of sealing plates 424, 426outwardly, away from one another and into a sealed position, as shown inFIG. 5 c.

In one embodiment, one or more of the bearings of pair 430 can besecured, attached, or at least partially housed within at least one ofsealing plates 424, 426 and/or drive member 428. According to oneembodiment, at least one of the bearings 430 a can be fixedly attachedto drive member 428, as depicted in the enlarged partial view of gateassembly 422 provided in FIG. 5d . As drive member 428 shifts downwardlyinto gate receiving space 416, one of the bearings 430 a from the paircan contact one of sealing plates 424, 426 (shown as plate 426 in FIG.5d ) and can move along a ramp (or slot) 427 therein. As the bearingtravels through the slot 427 (or along the ramp 427), outward pressureis exerted on sealing plate 426, thereby moving it in a direction asindicated by arrow 460. Although shown as including only a single pairof bearings 430, it should be understood that any number of bearings,positioned along the vertical length of drive member 428 and/or sealingmembers 424, 426 can be used.

When in a sealed position, as shown in FIG. 5c , at least a portion ofsealing plates 424, 426 engage or physically contact respective opposingsealing surface 414 a,b, to thereby form a substantially fluid tightseal. In one embodiment, each of sealing plates 424, 426 comprises aresilient seal 423, 425 for engaging sealing surfaces 414 a,b whensealing plates 424, 426 are in the sealed position. When drive member428 is shifted from the extended position, as shown in FIG. 5c , back tothe retracted position, as shown in FIG. 5b , sealing plates 424, 426retract towards one another into the unsealed position, as shown in FIG.5b . In the unsealed position, sealing plates 424, 426 are disengagedfrom opposing sealing surfaces 414 a,b, but may remain disposed withingate receiving space 416. In one embodiment, sealing plates 424, 426 canbe biased towards the unsealed position and can include at least onebiasing device 429 (e.g., a spring or springs) for biasing sealingplates 424, 426 toward the unsealed position.

Referring again to FIGS. 1a and 1b , the articles exiting thermalizationzone 12, and optionally passed through pressure adjustment zone 14 a, asdescribed above, can then be introduced into microwave heating zone 16.In microwave heating zone 16, the articles can be rapidly heated with aheating source that uses microwave energy. As used herein, the term“microwave energy” refers to electromagnetic energy having a frequencybetween 300 MHz and 30 GHz. In one embodiment, various configurations ofmicrowave heating zone 16 can utilize microwave energy having afrequency of about 915 MHz or a frequency of about 2.45 GHz, both ofwhich have been generally designated as industrial microwavefrequencies. In addition to microwave energy, microwave heating zone 16may optionally utilize one or more other heat sources such as, forexample, conductive or convective heating or other conventional heatingmethods or devices. However, at least about 85 percent, at least about90 percent, at least about 95 percent, or substantially all of theenergy used to heat the articles within microwave heating zone 16 can bemicrowave energy from a microwave source.

According to one embodiment, microwave heating zone 16 can be configuredto increase the temperature of the articles above a minimum thresholdtemperature. In one embodiment wherein microwave system 10 is configuredto sterilize a plurality of articles, the minimum threshold temperature(and operating temperature of microwave heating zone 16) can be at leastabout 120° C., at least about 121° C., at least about 122° C. and/or notmore than about 130° C., not more than about 128° C., or not more thanabout 126° C. Microwave heating zone 16 can be operated at approximatelyambient pressure, or it can include one or more pressurized microwavechambers operated at a pressure of at least about 5 psig, at least about10 psig, at least about 15 psig and/or not more than about 80 psig, notmore than about 60 psig, or not more than about 40 psig. In oneembodiment, the pressurized microwave chamber can be a liquid-filledchamber having an operating pressure such that the articles being heatedcan reach a temperature above the normal boiling point of the liquidmedium employed therein.

The articles passing through microwave heating zone 16 can be heated tothe desired temperature in a relatively short period of time, which, insome cases, may minimize damage or degradation of the articles. In oneembodiment, the articles passed through microwave heating zone 16 canhave an average residence time of at least about 5 seconds, at leastabout 20 seconds, at least about 60 seconds and/or not more than about10 minutes, not more than about 8 minutes, or not more than about 5minutes. In the same or other embodiments, microwave heating zone 16 canbe configured to increase the average temperature of the articles beingheated by at least about 20° C., at least about 30° C., at least about40° C., at least about 50° C., at least about 75° C. and/or not morethan about 150° C., not more than about 125° C., or not more than about100° C., at a heating rate of at least about 15° C. per minute (°C./min), at least about 25° C./min, at least about 35° C./min and/or notmore than about 75° C./min, not more than about 50° C./min, or not morethan about 40° C./min.

Turning now to FIG. 6a , one embodiment of a microwave heating zone 516is illustrated as generally comprising a microwave heating chamber 520,at least one microwave generator 512 for generating microwave energy anda microwave distribution system 514 for directing at least a portion ofthe microwave energy from generator 512 to microwave chamber 520.Microwave distribution system 514 comprises a plurality of waveguidesegments 518 and one or more microwave launchers, shown as launchers 522a-f in FIG. 6a , for discharging microwave energy into the interior ofmicrowave chamber 520. As shown in FIG. 6a , microwave heating zone 516can further comprise a conveyance system 540 for transporting articles550 to be heated through microwave chamber 520. Each of the componentsof microwave heating zone 516, according to various embodiments of thepresent invention, are now discussed in detail immediately below.

Microwave generator 512 can be any suitable device for generatingmicrowave energy of a desired wavelength (λ). Examples of suitable typesof microwave generators can include, but are not limited to, magnetrons,klystrons, traveling wave tubes, and gyrotrons. Although illustrated inFIG. 6a as including a single generator 512, it should be understoodthat microwave heating system 516 can include any number of generatorsarranged in any suitable configuration. For example, in one embodiment,microwave heating zone 516 can include at least 1, at least 2, at least3 and/or not more than 5, not more than 4, or not more than 3 microwavegenerators, depending on the size and arrangement of microwavedistribution system 514. Specific embodiments of a microwave heatingzone including multiple generators will be discussed in detail below.

Microwave chamber 520 can be any chamber or vessel configured to receivea plurality of articles. Microwave chamber 520 can be of any size andmay have one of a variety of different cross-sectional shapes. Forexample, in one embodiment, chamber 520 can have a generally circular orelliptical cross-section, while, in other embodiments, can have agenerally square, rectangular, or polygonal cross-sectional shape. Inone embodiment, microwave chamber 520 can be a pressurized chamber and,in the same or other embodiments, can be configured to be at leastpartially filled with a liquid medium (a liquid-filled chamber).Microwave chamber 520 can also be configured to receive at least aportion of the microwave energy discharged from one or more microwavelaunchers 522 and, in one embodiment, can be configured to permit thecreation of a stable (or standing) wave pattern therein. In oneembodiment, at least one dimension of microwave chamber 520 can be atleast about 0.30λ, at least about 0.40λ, or at least about 0.50λ,wherein λ is the wavelength of the microwave energy discharged therein.

Microwave distribution system 514 comprises a plurality of waveguides orwaveguide segments 518 for directing at least a portion of the microwaveenergy from generator 512 to microwave chamber 520. Waveguides 518 canbe designed and constructed to propagate microwave energy in a specificpredominant mode, which may be the same as or different than the mode ofthe microwave energy generated by generator 512. As used herein, theterm “mode” refers to a generally fixed cross-sectional field pattern ofmicrowave energy. In one embodiment of the present invention, waveguides518 can be configured to propagate microwave energy in a TE_(xy) mode,wherein x and y are integers in the range of from 0 to 5. In anotherembodiment of the present invention, waveguides 518 can be configured topropagate microwave energy in a TM_(ab) mode, wherein a and b areintegers in the range of from 0 to 5. It should be understood that, asused herein, the above-defined ranges of a, b, x, and y values as usedto describe a mode of microwave propagation are applicable throughoutthis description. In one embodiment, the predominant mode of microwaveenergy propagated through waveguides 518 and/or discharged via launchers522 a-f can be selected from the group consisting of TE₁₀, TM₀₁, andTE₁₁.

As shown in FIG. 6a , microwave distribution system 514 furthercomprises one or more microwave launchers 522 a-f, each defining atleast one launch opening 524 a-f for discharging microwave energy intomicrowave chamber 520. Although illustrated in FIG. 6a as comprising sixmicrowave launchers 522 a-f, it should be understood that microwavedistribution system 514 can include any suitable number of launchersarranged in any desirable configuration. For example, microwavedistribution system 514 can include at least 1, at least 2, at least 3,at least 4 and/or not more than 50, not more than 30, or not more than20 microwave launchers. Launchers 522 a-f can be the same or differenttypes of launchers and, in one embodiment, at least one of launchers 522a-f can be replaced with a reflective surface (not shown) for reflectingat least a portion of the microwave energy discharged from the otherlaunchers 522 into microwave heating chamber 520.

When microwave distribution system 514 includes two or more launchers,at least some of the launchers may be disposed on generally the sameside of microwave chamber 520. As used herein, the term “same-sidelaunchers” refers to two or more launchers positioned on generally thesame side of a microwave chamber. Two or more of the same-side launchersmay also be axially spaced from one another. As used herein, the term“axially spaced” denotes spacing in the direction of conveyance of thearticles through the microwave system (i.e., spacing in the direction ofextension of the convey axis). Additionally, one or more launchers 522may also be laterally spaced from one or more other launchers 522 of thesystem. As used herein, the term “laterally spaced” shall denote spacingin the direction perpendicular to the direction of conveyance of thearticles through the microwave system (i.e., spacing perpendicular tothe direction of extension of the convey axis). For example, in FIG. 6a, launchers 522 a-c and 522 d-f are disposed on respective first andsecond sides 521 a,b of microwave chamber 520 and launcher 522 a isaxially spaced from launcher 522 b and 522 c, just as launcher 522 e isaxially spaced from launchers 522 f and 522 d.

Additionally, as shown in the embodiment depicted in FIG. 6a , microwavedistribution system 514 can comprise at least two (e.g., two or more)pairs of oppositely disposed or opposed launchers. As used herein, theterm “opposed launchers” refers to two or more launchers positioned ongenerally opposite sides of a microwave chamber. In one embodiment, theopposed launchers may be oppositely facing. As used herein with respectto opposed microwave launchers, the term “oppositely facing” shalldenote launchers whose central launch axes are substantially alignedwith one another. For simplicity, central launch axis 523 c of launcher522 c and central launch axis 523 d of launcher 522 d are the onlycentral launch axes illustrated in FIG. 6a . However, it should beunderstood that each of launchers 522 a-f include a similar launch axes.

Opposed launchers may be generally aligned with one another, or may bestaggered from one or more other launchers disposed on the opposite sideof microwave chamber 520. In one embodiment, a pair of opposed launchersmay be a staggered pair of launchers, such that the discharge openings524 of the launchers 522 are not in substantial alignment with oneanother. Launchers 522 a and 522 e constitute one exemplary pair ofopposed launchers arranged in a staggered configuration. Staggeredopposed launchers may be axially or laterally staggered from oneanother. As used herein with respect to opposed microwave launchers, theterm “axially staggered” shall denote launchers whose central launchaxes are axially spaced from one another. As used herein with respect toopposed microwave launchers, the term “laterally staggered” shall denotelaunchers whose central launch axes are laterally spaced from oneanother. In another embodiment, a pair of opposed launchers may bedirectly opposite launchers, such that the discharge openings of thelauncher pair are substantially aligned. For example, launchers 522 cand 522 d shown in FIG. 6a are configured as a pair of oppositelaunchers.

In some embodiments, microwave heating zone 516 can include two or moreconvey lines operating simultaneously with one another. An exemplarymulti-line conveyance system 540 is shown in FIGS. 6b and 6c . As shownin FIGS. 6b and 6c , conveyance system 540 can be configured totransport a plurality of articles 550 in a convey direction generallyrepresented by arrow 560 in FIG. 6b . In one embodiment, conveyancesystem 540 can include at least two laterally spaced, substantiallyparallel convey lines, such as, for example, first, second, and thirdconvey lines 542 a-c shown in FIG. 6b . Convey lines 542 a-c can, in oneembodiment, comprise individual conveyance systems, while, in anotherembodiment, each of convey lines 542 a-c can be portions of an overallconveyance system. Conveyance system 540 and/or convey lines 542 a-c canbe any suitable type of conveyor or conveyance system, including thosediscussed in detail previously.

Microwave heating system 516 depicted in FIGS. 6b and 6c includes aplurality of microwave launchers 522 that can be divided or organizedinto at least two groups of two or more microwave launchers. Each offirst, second, and third convey lines 542 a-c can be configured toreceive microwave energy from respective first, second, and third groupsof microwave launchers. In one embodiment, a “group” of launchers canrefer to two or more axially spaced launchers, generally position alongthe convey direction (e.g., launcher group 522 a-d, launcher group 522e-h, and/or launcher group 522 i-l shown in FIG. 6b ), while, in theanother embodiment, a “group” of launchers can include one or more pairsof opposed launchers positioned on different sides of a microwavechamber (e.g., groups that include pair of launchers 522 a and 522 m,the group that includes pair of launchers 522 b and 522 n, group thatincludes pair of launchers 522 c and 522 o, and group that includes pairof launchers 522 d and 522 p, as shown in FIG. 6c ). When the group oflaunchers comprises one or more pairs of opposed launchers, thelaunchers can be arranged in a staggered configuration (not shown) orcan be directly opposite one another (e.g. oppositely facing), asillustrated in FIG. 6c . According to one embodiment, at least onegenerator, shown as generator 512 a in FIG. 6b , can be configured toprovide microwave energy to at least one group of microwave launchers.

As particularly shown in FIG. 6b , individual microwave launchers 522 ofadjacent convey lines 542 can be arranged in a staggered configurationrelative to one another in the convey direction. In one embodiment, oneor more same-side microwave launchers 522 a-l may be axially staggeredfrom one another. For example, in the embodiment shown in FIG. 6b ,launchers 522 a-d associated with first convey line 542 a are arrangedin a staggered configuration relative to each of respective launchers522 e-h associated with second convey line 542 b with respect to and/oralong the convey direction 560. As used herein with respect to same-sidemicrowave launchers, the term “axially staggered” shall denote launchersthat are axially spaced from one another by distance greater that ½ themaximum axial dimension of the launch openings of the launchers. As usedherein with respect to same-side microwave launchers, the term“laterally staggered” shall denote launchers that are laterally spacedfrom one another by a distance greater that ½ the maximum lateraldimension of the launch openings of the launchers.

Additionally, in the same or another embodiment, the microwave launchersassociated with the non-adjacent convey lines (e.g., first and thirdconvey lines 542 a,c) can be arranged in a substantially alignedconfiguration relative to one another, as illustrated by the arrangementof launchers 522 a-d relative to launchers 522 i-l shown in FIG. 6b .Alternatively, at least a portion of the launchers 522 i-l associatedwith third convey line 542 c may be staggered with respect to launchers522 a-d of first convey line 542 a and/or second convey line 542 b(embodiment not shown). Although generally depicted in FIG. 6b asincluding little to no space between launchers of adjacent convey lines,it should be understood that, in one embodiment, that some space mayexist between launchers of adjacent lines (e.g., launchers 522 a and 522e, launchers 522 b and 522 f, etc.). Further, individual launchers 522can have any suitable design or configuration and, in one embodiment,can include at least one feature from one or more embodiments of thepresent invention which will be described in detail herein.

Turning now to FIG. 7a , a partial view of one embodiment of a microwaveheating zone 616 is shown. Microwave heating zone 616 includes at leastone microwave launcher 622 that defines a launch opening 624 fordischarging energy into a microwave chamber 620. As shown in FIG. 7a ,microwave launcher 622 is configured to discharge microwave energy alonga central launch axis 660 toward a conveyance system 640 configured totransport a plurality of articles 650 within microwave chamber 620 alonga convey axis 642.

In one embodiment, central launch axis 660 can be tilted such that alaunch tilt angle, β, is defined between central launch axis 660 and aplane normal to convey axis 642, illustrated as plane 662 in FIG. 7a .According to one embodiment, launch tilt angle β can be at least about2°, at least about 4°, at least about 5° and/or not more than about 15°,not more than about 10°, or not more than about 8°.

Turning now to FIG. 7b , another embodiment of a microwave heatingsystem 616 is shown as including two or more launchers 622 a-c, eachconfigured to discharge energy into microwave chamber 620 alongrespective tilted central launch axes 660 a-c. In one embodiment whereinmicrowave heating system 616 includes two or more tilted launchers, thecentral launch axes of the launchers, especially the same-sidelaunchers, can be substantially parallel to one another, as generallyillustrated by central launch axes 660 a,b of launchers 622 a,b shown inFIG. 7b . As used herein, the term “substantially parallel” means within5° of being parallel. In the same or another embodiment, the centrallaunch axes of two or more launchers, especially opposed launchers,within microwave heating zone 616 can be substantially parallel orsubstantially aligned, as illustrated by launch axes 660 a,c ofmicrowave launchers 622 a,c in FIG. 7b . When microwave heating zone 616comprises n tilted microwave launchers having central launch axesoriented as described above, each launcher can define a respectivelaunch tilt angle, β_(n), within the ranges discussed previously. In oneembodiment, each of the launch tilt angles β_(n) of each launcher may besubstantially the same, while, in another embodiment, at least one ofthe launch tilt angles β_(n) can be substantially different than one ormore other launch tilt angles.

Referring back to FIG. 6a , at least one of launch openings 524 a-f oflaunchers 522 a-f of microwave system 516 can be at least partiallycovered by a substantially microwave-transparent window 526 a-f disposedbetween each launch opening 524 a-f and microwave chamber 520.Microwave-transparent windows 526 a-f can be operable to prevent fluidflow between microwave chamber 520 and microwave launchers 522 a-f whilestill permitting a substantial portion of the microwave energy fromlaunchers 522 a-f to pass therethrough. Windows 526 a-f can be made ofany suitable material, including, but not limited to one or morethermoplastic or glass material such as glass-filled Teflon,polytetrafluoroethylene (PTFE), poly(methyl methacrylate (PMMA),polyetherimide (PEI), aluminum oxide, glass, and combinations thereof.In one embodiment, windows 526 a-f can have an average thickness of atleast about 4 mm, at least about 6 mm, at least about 8 mm and/or notmore than about 20 mm, not more than about 16 mm, or not more than about12 mm and can withstand a pressure difference of at least about 40 psi,at least about 50 psi, at least about 75 psi and/or not more than about200 psi, not more than about 150 psi, or not more than about 120 psiwithout breaking, cracking, or otherwise failing.

Several embodiments of suitable configurations for microwave launcherwindows are generally depicted in FIGS. 8a-c . As shown in FIGS. 8a-c ,each of microwave windows 726 define a chamber-side surface 725 that canoptionally define at least a portion of the sidewall 721 of microwavechamber 720. According to one embodiment shown in FIG. 1, chamber-sidesurface 725 of window 726 can be configured such that at least about 50percent, at least about 65 percent, at least about 75 percent, at leastabout 85 percent, or at least about 95 percent of the total surface areaof chamber-side surface 725 is oriented at a tilt angle, α, from thehorizontal. Tilt angle α can be at least about 2°, at least about 4°, atleast about 8°, at least about 10° and/or not more than about 45°, notmore than about 30°, or not more than about 15° from the horizontal,illustrated as dashed line 762. In other embodiments, the tilt angle, a,may also be defined between the axis of elongation 762 of microwavechamber 720 and/or an axis of convey (not shown in FIGS. 8a-c ) when,for example, these axes are parallel to the horizontal.

Chamber-side surface 725 of window 726 can be oriented from thehorizontal regardless of whether or not launcher 722 is oriented with alaunch tilt angle as described above. In one embodiment, window 726 canbe substantially planar and sloped from the horizontal (as shown in FIG.8a ), while, in the same or another embodiment, chamber-side surface 725of window 726 can include one or more convexities (as shown in FIG. 8b )or concavities (as shown in FIG. 8c ). When chamber-side surface 725 isnot substantially planar, one or more (or n) total tilt angles may beformed as described above. Depending on the exact configuration ofchamber-side surface 725, the multiple tilt angles formed thereby may bethe same as or different than other tilt angles formed by the samesurface 725.

As discussed previously, the microwave launchers 522 a-f depicted inFIG. 6a may be of any suitable configuration. Several views of amicrowave launcher 822 configured according to one embodiment of thepresent invention are provided in FIGS. 9a-f . Referring initially toFIG. 9a , microwave launcher 822 is illustrated as comprising a set ofopposing sidewalls 832 a,b and a set of opposing end walls 834 a,b,which collectively define a substantially rectangular launch opening838. When launch opening 838 comprises a rectangular-shaped opening, itcan have a width (W₁) and a depth (D₁) defined, at least in part, by theterminal edges of sidewalls 832 a,b and 834 a,b, respectively. In oneembodiment, sidewalls 832 a,b can be broader than end walls 834 a,b suchthat the length of the lower terminal edge of side walls 832 a,b, shownas W₁ in FIG. 9a , can be greater than the length of the lower terminaledge of end walls 834 a,b, depicted in FIG. 9a with the identifier D₁.As shown in FIG. 9a , the elongated portion of side walls 832 a,b andend walls 834 a,b can also collectively define a pathway 837 throughwhich microwave energy can propagate as it passes from the microwaveinlet 836 to the at least one launch opening 838 defined by launcher822.

When used to discharge microwave energy into a microwave chamber, launchopening 838 can be can be elongated in the direction of extension of themicrowave chamber (not shown) or in the direction of convey of thearticles therein. For example, in one embodiment, side walls 832 a,b andend walls 834 a,b of launcher 822 can be configured such that themaximum dimension of launch opening 838 (shown in FIG. 9a as W₁) can bealigned substantially parallel to the direction of extension of themicrowave chamber and/or to the direction of convey of articles passingtherethrough. In this embodiment, the terminal edges of side walls 832a,b can be oriented parallel to the direction of extension (or thedirection of convey), while the terminal edges of end walls 834 a,b maybe aligned substantially perpendicular to the direction of extension orconvey within the microwave chamber (not shown in FIG. 9).

FIGS. 9b and 9c respectively provide views of a sidewall 832 and endwall 834 of microwave launcher 822 illustrated in FIG. 9a . It should beunderstood that, while only one of the side or end walls 832, 834 areshown in FIGS. 9b and 9c , the other of the pair could have a similarconfiguration. In one embodiment, at least one of side wall 832 and endwall 834 can be flared such that the inlet dimension (width W₀ or depthD₀) is smaller than the outlet dimension (width W₁ or depth D₁), asrespectively illustrated in FIGS. 9b and 9c . When flared, each of sideand end walls 832, 834 define respective width and depth flare angles,θ_(w) and θ_(d), as shown in FIGS. 9b and 9c . In one embodiment, widthand/or depth flare angles θ_(w) and/or θ_(d) can be at least about 2°,at least about 5°, at least about 10°, or at least about 15° and/or notmore than about 45°, not more than about 30°, or not more than about15°. In one embodiment, the width and depth flare angles θ_(w) and θ_(d)can be the same, while, in another embodiment, the values for θ_(w) andθ_(d) may be different.

According to one embodiment, depth flare angle θ_(d) can be smaller thanwidth flare angle θ_(w). In certain embodiments, depth flare angle θ_(d)can be not more than about 0°, such that the inlet depth D₀ and theoutlet dimension D₁ of microwave launcher 822 are substantially thesame, as illustrated in the embodiment depicted in FIG. 9d . In anotherembodiment, the depth flare angle θ_(d) may be less than 0°, such thatD₁ is smaller than D₀, as shown in FIG. 9e . When microwave launcher 822comprises a depth flare angle less than 0° and/or the depth D₁ of launchopening 838 is smaller than the depth D₀ of microwave inlet 836,microwave launcher 822 can be a tapered launcher having a generallyinverse profile. In one embodiment wherein microwave launcher 822comprises n launch openings, between 1 and n of the openings can have adepth and/or width less than or equal to the depth and/or width of theinlet of the launcher. Further embodiments of multi-opening launcherswill be discussed in detail below.

According to one embodiment of the present invention, the depth D₁ oflaunch opening 838 can be no more than about 0.625λ, not more than about0.5λ, not more than about 0.4λ, not more than about 0.35λ, or not morethan about 0.25λ, wherein λ is the wavelength of the predominant mode ofmicrowave energy discharged from launch opening 838. Although notwishing to be bound by theory, it is believed that minimizing the depthD₁ of launch opening 838, the microwave field created proximate launchopening 838 is more stable and uniform than would be created bylaunchers having greater depths. In one embodiment wherein microwavelauncher 822 comprises n launch openings, the depth of each launchopening, d_(n), can be not more than about 0.625λ, not more than about0.5λ, not more than about 0.4λ, not more than about 0.35λ, or not morethan about 0.25λ. When microwave launcher 822 has multiple openings,each opening can have a depth that is the same or different than one ormore of the other launch openings of the same launcher.

Referring now to FIGS. 10a-c , another embodiment of a microwavelauncher 922 suitable for use in the microwave heating systems describedherein is illustrated as comprising a single microwave inlet 936 and twoor more launch openings, shown as launch or discharge openings 938 a-c,for discharging microwave energy therefrom. Microwave launcher 922illustrated in FIGS. 10a-c includes first, second, and third spacedapart launch openings 938 a-c, which are laterally spaced from oneanother. Although described herein as defining three launch openings, itshould be understood that launcher 922 can include any suitable numberof launch openings including at least 2, at least 3, at least 4 and/ornot more than 10, not more than 8, or not more than 6. The spacingbetween each of first, second, and third launch openings 938 a-c can beat least about 0.05λ, at least about 0.075λ, or at least about 0.10λand/or not more than about 0.25λ, not more than about 0.15λ, or not morethan about 0.1λ, wherein λ is the wavelength of the predominant mode ofmicrowave energy discharged from launcher 922.

In one embodiment, each of first, second, and third launch openings areseparated by one or more dividing septum (or septa) 940 a,b disposedwithin the interior of launcher 922, as shown in FIGS. 10a-c . Septa 940a,b typically have a thickness equal to the desired spacing between thedischarge openings 938 a-c. When microwave launcher comprises n septa,microwave launcher 922 defines (n+1) separated launch openings and (n+1)separate microwave pathways 937 a-c defined between microwave inlet 836and each of launch openings 938 a-c, as particularly shown in FIG. 10c .As shown in FIG. 10c , each of microwave pathways 937 a-c has a length,L₁-L₃, which extends from inlet 936 to a point perpendicular withrespective launch opening 938 a-c. Each of L₁-L₃ can be substantiallythe same, or at least one of L₁, L₂, and L₃ can be substantiallydifferent. According to one embodiment, particularly shown in FIG. 10c ,one or more pathways 937 a-c can be longer than one or more otherpathways 937 a-c.

When one or more pathways 937 a-c are of different lengths than one ormore other pathways, the dimensions (L₁, L₂, and/or L₃) of pathways 937a-c may be adjusted such that the phase velocity of the microwave energypropagating therethrough accelerates at a more rapid pace within thelonger microwave pathways (e.g., L₁ and L₃ in FIG. 10c ) than throughthe shorter pathways (e.g., L₂ in FIG. 10c ). Although not wishing to bebound by theory, it is hypothesized that such adjusting can be carriedout to ensure uniform synchronization of individual wave portions,thereby creating a uniform wave front as the microwave energy isdischarged into chamber 520. When microwave launcher 922 includes asingle septum, only two microwave pathways are created (embodiment notshown) and the length of each pathway is substantially the same.Consequently, little or no control of the phase velocity of microwaveenergy passing through the equal length pathways may be needed.

In the same or another embodiment, each of launch openings 938 a-c candefine a depth, d₁₋₃, as generally depicted in FIG. 10b . In oneembodiment, each of depths d₁ through d₃ can be substantially the same,while, in another embodiment, at least one of the depths d₁-d₃ can bedifferent. As discussed previously, one or more of d₁-d₃ can be not morethan about 0.625λ, not more than about 0.5λ, not more than about 0.4λ,not more than about 0.35λ, or not more than about 0.25λ, wherein λ isthe wavelength of the predominant mode of microwave energy dischargedfrom launch opening 938 a-c. In addition, in one embodiment, at leastone of d₁-d₃ can be less than or equal to the depth d₀ of inlet 936 asdiscussed in detail previously. As shown in FIG. 10b , the depths, d₁₋₃,of each of launch openings 938 a-c do not include the thickness of septa940 a,b, when present.

Referring again to FIG. 6a , in one embodiment, the microwavedistribution system 514 of microwave heating zone 516 can include atleast one microwave distribution manifold 525 a,b for allocating ordistributing microwave energy into chamber 520 via a plurality oflaunchers 522 a-c and 522 d-f. In one embodiment, microwave distributionmanifold 525 a,b can include at least three microwave allocation devicesconfigured to divide the microwave energy from generator 512 into two ormore separate portions prior to being discharged from at least some ofmicrowave launchers 522 a-f. As used herein, the term “microwaveallocation device” refers to any device or item operable to dividemicrowave energy into two or more separate portions, according to apredetermined ratio. As used herein, the term “predetermined powerratio” refers to the ratio of the amount of power of each resultantseparate portion exiting a specific microwave allocation device. Forexample, a microwave allocation device configured to divide the powerpassing therethrough at a 1:1 power ratio would be configured to dividethe power introduced therein into two substantially equal portions.

However, in one embodiment of the present invention, at least one of themicrowave allocation devices, shown as inductive irises 570 a-h and“T-shaped” or two-way splitter 572 in FIG. 6a , of microwavedistribution system 514 can be configured to have a predetermined powerratio that is not 1:1. For example, one or more of the microwaveallocation devices 570 a-h or 572 can be configured to divide themicrowave energy passing therethrough according to a predetermined powerratio of at least about 1:1.5, at least about 1:2, at least about 1:3and/or not more than about 1:10, not more than about 1:8, or not morethan about 1:6.

Each of the allocation devices 570 a 2-h and/or 5 employed by microwavedistribution system 514 may be configured to discharge energy accordingto the same ratio, or one or more of allocation devices 570 a-h can beconfigured at a different power ratio. Allocation devices 570 a-h and572 can be configured such that substantially the same amount of poweris discharged from each of launchers 522 a-f, while, in anotherembodiment, the allocation devices 570 a-h and 572 can be collectivelydesigned such that more power is diverted to and discharged from one ormore launchers 522 a-f, with less power being discharged through theremainder of the launchers 522 a-f. The specific power ratios utilizedeach of microwave allocation devices 570 a-h and 572, as well as thepattern or overall configuration of microwave energy allocation withinthe system, can depend on a variety of factors including, for example,the type of articles being heated, the desired operating conditions ofthe microwave heating zone 516, and other similar factors.

In operation, an initial quantity of microwave power can be introducedinto microwave distribution system 514 and can be divided into twoportions as it passes through splitter 572. In one embodiment, the twoportions of microwave energy exiting splitter 572 can be approximatelyof approximately the same power, while, in another embodiment, one ofthe two portions may have more power than the other. As shown in FIG. 6a, each portion may pass to a respective manifold 525 a,b, optionallypassing through a phase shifting device 530 prior to entering manifold525 a,b. Described now with respect to microwave distribution manifold525 a, it should be understood that analogous operation is applicable tothe lower manifold 525 b shown in FIG. 6 a.

The microwave power exiting splitter 572 and optionally phase shiftingdevice 530 (embodiments of which will be discussed in detail below) maythen pass through a microwave allocation device, shown as iris 570 a,whereupon the power can be divided into a first launch microwavefraction and a first distribution microwave fraction. The first launchmicrowave fraction can be directed toward launcher 522 a and can bedischarged via outlet 524 a The first distribution microwave fractioncan be propagated down waveguide 518 toward the additional microwavelaunchers 522 b,c. According to one embodiment, the power ratio of thefirst launch microwave fraction to the first distribution microwavefraction exiting iris 570 a can be not more than about 1:1, not morethan about 0.95:1, not more than about 0.90:1, not more than 0.80:1, notmore than about 0.70:1 or not more than 0.60:1. In one embodiment, thepower ratio of the first launch microwave fraction to the firstdistribution microwave fraction is not 1:1.

As the first distribution microwave fraction propagates toward launchers522 b,c, it can subsequently be divided into a second launch microwavefraction directed toward launcher 522 b to be discharged via launchoutlet 524 b, and a second distribution microwave fraction thatpropagates down waveguide 518 toward launcher 522 c. In one embodiment,the ratio of second launch microwave fraction to second distributionmicrowave fraction can be at least about 0.80:1, at least about 0.90:1,at least about 0.95:1 and/or not more than about 1.2:1, not more thanabout 1.1:1, not more than about 1.05:1, or can be approximately 1:1.Subsequently, the remainder of the microwave energy (e.g., the entiretyof the second distribution microwave fraction) can then be directed tothe final microwave launcher 522 c and discharged from launch outlet 524c.

According to another embodiment (not shown in FIG. 6a ), microwavedistribution system 514 can include a microwave distribution manifold525 a,b having more than three launchers. For example, when microwavedistribution manifold 525 includes n launchers, all but the (n−1)th stepof dividing can be carried out such that the ratio of the launchmicrowave fraction to the distribution microwave fraction is not 1:1.For each of the steps except the (n−1)th step, the power ratio can benot more than about 1:1, not more than about 0.95:1, not more than about0.90:1, not more than 0.80:1, not more than about 0.70:1 or not morethan 0.60:1, while the (n−1)th dividing step can be carried out suchthat the ratio of the launch microwave fraction to second distributionmicrowave fraction can be at least about 0.80:1, at least about 0.90:1,at least about 0.95:1 and/or not more than about 1.2:1, not more thanabout 1.1:1, not more than about 1.05:1, or can be approximately 1:1.The (n−1)th distribution microwave fraction can then be sent, in itsmajority or entirety, as an nth launch microwave fraction to bedischarged to the microwave chamber via the nth microwave launcher.

In addition to one or more irises 570 a-h positioned within microwavedistribution system 514, one or more of launchers 522 can also includeat least one inductive iris disposed within the launcher, as shown inone embodiment illustrated in FIGS. 11a and 11b . Alternatively, one ormore of irises 570 b and/or 570 d may be disposed within launchers 522 aand/or 522 b, respectively, rather than be disposed within a waveguideas shown in FIG. 6 a.

One embodiment of a microwave launcher 1022 including an inductive irisdisposed therein is shown in FIG. 11a . Launcher 1022 may include atleast one inductive iris 1070 located between its microwave inlet 1036and one or more launch openings 1038, as generally illustrated in FIGS.11a and 11b . As shown in FIGS. 11a and 11b , iris 1070 may be definedby a pair of inductive iris panels 1072 a,b disposed on opposite sidesof launcher 1022. Although illustrated as being coupled to narroweropposing end walls 1034 a,b of launcher 1022, it should be understoodthat first and second iris panels 1072 a,b could also be coupled tobroader opposing side walls 1032 a,b of launcher 1022. As shown in FIGS.11a and 11b , first and second iris panels 1072 a,b extend inwardly intothe microwave pathway 1037 defined between microwave inlet 1036 andlaunch opening 1038 in a direction that is generally transverse to thedirection of microwave propagation through pathway 1037. In oneembodiment, iris panels obstruct at least about 25 percent, at leastabout 40 percent, or at least about 50 percent and/or not more thanabout 75 percent, not more than about 60 percent, or not more than about55 percent of the total area of microwave pathway 1037 at the locationat which they are disposed. When microwave launcher 1022 comprises twoor more launch openings, as shown in FIG. 11c , first and second irispanels 1072 a,b can be configured to obstruct at least a portion of eachof the launch openings 1038 a-c of the launcher 1022.

As shown in FIG. 11a , first and second iris panels 1072 a,b can besubstantially co-planar and can be oriented substantially normal to thecentral launch axis of microwave launcher 1022. In certain embodiments,the iris panels 1072 a,b may be spaced from both the microwave inlet1036 and the launch opening 1038 of microwave launcher 1022. Forexample, the iris panels 1072 a,b can be spaced from microwave inlet1036 of launcher 1022 by at least about 10 percent, at least about 25percent, or at least about 35 percent of the minimum distance betweenmicrowave inlet 1036 and launch opening 1038 of launcher 1022. Further,iris panels 1072 a,b can be spaced from launch opening 1038 of launcher1022 by at least about 10 percent, 25 percent, or 35 percent of themaximum distance (L) measured between microwave inlet 1036 and launchopening 1038 of launcher 1022.

Turning again to FIG. 6a , microwave distribution system 514 isillustrated as further comprise one or more devices or for increasingthe uniformity and/or strength of the microwave field created withinmicrowave heating chamber 520. For example, in one embodiment, microwavedistribution system 514 can include one or more devices designed tomodify and/or control the location and strength of the constructiveinterference bands of the microwave field created within each ofindividual heating zones 580 a-c, which are respectively defined betweenpairs of launchers 522 a and 522 f, 522 b and 522 e, and 522 c and 522d. In one embodiment, such a device can be a phase shifting device,schematically represented in FIG. 6a as device 530, operable tocyclically shift the phase of the microwave energy passing therethrough.

As the articles 550 move along conveyance system 540 within microwavechamber 520, each article 550 can have an average residence time (τ),within each individual heating zone 580 a-c, of at least about 2seconds, at least about 10 seconds, at least about 15 seconds and/or notmore than about 1 minute, not more than about 45 seconds, or not morethan about 30 seconds. In one embodiment, the average residence time (τ)for articles 550 can be greater than the phase shifting rate (t) forwhich phase shifting device 530 is configured. For example, the ratio ofthe average residence time of the articles passing through one ofindividual heating zones 580 a-c to the phase shifting rate of device530 (τ:t) can be at least about 2:1, at least about 3:1, at least about4:1, at least about 5:1 and/or not more than about 12:1, not more thanabout 10:1, or not more than about 8:1.

Phase shifting device 530 can be any suitable device for rapidly andcyclically shifting the phase of microwave energy passing throughmicrowave distribution system 514. According to one embodiment, phaseshifting device 530 can be configured to shift the microwave energypassing therethrough at a phase shifting rate (t) of at least about 1.5cycles per second, at least about 1.75 cycles per second, or at leastabout 2.0 cycles per second and/or not more than about 10 cycles persecond, not more than about 8 cycles per second, and/or not more thanabout 6 cycles per second. As used herein, the term “phase shiftingrate” refers to the number of complete phase shift cycles completed persecond. A “complete phase shift cycle” refers to a phase shift from 0°to 180° and back to 0°. Although shown as including a single phaseshifting device 530, it should be understood that any suitable number ofphase shifting devices can be utilized within microwave distributionsystem 514.

In one embodiment, phase shifting device 530 can comprise a plunger-typetuning device operable to be moved in a generally linear (e.g.,up-and-down motion) within a cylinder to thereby cause the phase of themicrowave energy passing therethrough to be cyclically shifted. FIGS.12a and 12b illustrate two embodiments of a plunger-type tuning device1130 a,b suitable for use in microwave distribution system 514. FIG. 12adepicts a single-plunger phase shifting device 1130 a that includes oneplunger 1132 operable to move within a single cylinder 1134 via anautomatic driver 1136. FIG. 12b illustrates another embodiment of aphase shifting device that comprises a multi-plunger phase shiftingdevice that includes a plurality of plungers 1132 a-d disposed andoperable to moved within several corresponding cylinders 1134 a-d.Plungers 1132 a-d can be driven by a single automatic driver 1136, whichcan be connected to each of plungers 1132 a-d via a rotatable cam shaft1138. Either of plunger-type tuning devices 1130 a,b can be connected toa coupler, such as, for example, a short slot hybrid coupler (not shownin FIGS. 12a and 12b ) and can be employed in microwave distributionsystem 514 as a phase shifting device 530 as described above.

Another embodiment of a suitable phase shifting device is depicted inFIGS. 13a-e . In contrast to the phase shifting or tuning devicesillustrated in FIGS. 12a and 12b , the phase shifting devicesillustrated in FIGS. 13a-e are rotatable phase shifting devices. Forexample, as shown in FIGS. 13a-c , one embodiment of a rotatable phaseshifting device 1230, also referred to as a variable phase shortcircuit, can comprise a fixed section 1210 defining a firstsubstantially rectangular opening 1212 and a rotatable section 1240positioned proximate said first opening 1212. As shown in FIG. 13a , agap 1213 can be defined between rotatable section 1240 and fixed section1210 and, in one embodiment, a microwave choke (not shown) can be atleast partially disposed within gap 1213 for preventing the leakage ofmicrowave energy from fixed and rotatable sections 1210 and 1240.

Rotatable section 1240 comprises a housing 1242 and a plurality ofspaced apart, substantially parallel plates 1244 a-d received withinhousing 1242. As shown in FIG. 13a , housing 1242 comprises a first end1243 a and a second end 1243 b and first end 1243 a defines a secondopening 1246 adjacent to first rectangular opening 1212 of fixed section1210. As indicated by arrows 1290, 1292 in FIG. 13a , rotatable section1240 can be configured to be rotated relative to fixed section 1210about an axis of rotation 1211 extending through first and secondopenings 1212, 1246, as generally shown in FIGS. 13a -c.

As particularly shown in FIGS. 13b and 13c , housing 1242 has a length(L_(H)), a width (W_(H)), and a depth (D_(H)). In one embodiment, atleast one of L_(H), W_(H), and D_(H) are at least about 0.5λ, at leastabout 0.65λ, at least about 0.75λ and/or not more than about 1λ, notmore than about 0.9λ, or not more than about 0.75λ, wherein λ is thewavelength of the microwave energy which variable phase short circuit1230 is configured to pass between first and second openings 1212 and1246. In one embodiment, at least one of W_(H) and D_(H) are at leastabout 0.5λ and both are not more than about λ. As generally shown inFIGS. 13a-c , the cross-sectional shape of housing 1242 is substantiallysquare, such that the ratio of W_(H):D_(H) is not more than about 1.5:1,not more than about 1.25:1, or not more than about 1.1:1.

Fixed section 1210 can be any suitable shape or size and may comprise acircular or a rectangular waveguide. In one embodiment shown in FIG. 13d, first substantially rectangular opening 1212 can have a width (W_(R))and a depth (D_(R)) such that the ratio of W_(R):D_(R) is at least about1.1:1, at least about 1.25:1, or at least about 1.5:1. The width offirst openings 1212 of fixed section 1210 and the width of secondopening 1246 of rotatable section 1240 are substantially the same, suchthat the ratio W_(H):W_(R) is at least about 0.85:1, at least about0.95:1, or at least about 0.98:1 and/or not more than about 1.15:1, notmore than about 1.05:1, or not more than about 1.01:1.

As generally shown in FIG. 13a , each of plates 1244 a-d can be coupledto second end 1243 b of housing 1242 and can extend generally towardfirst end 1243 a of housing 1242 in a direction toward first and secondopenings 1212 and 1244. Each of plates 1244 a-d can have an extensiondistance or length, shown as L_(e) in FIG. 13b , of at least about 0.1λ,at least about 0.2λ, at least about 0.25λ and/or not more than about0.5λ, not more than about 0.35λ, or not more than about 0.30λ.Additionally, as particularly shown in FIG. 13c , one or more of plates1244 a-d can have a thickness, k, of at least about 0.01λ, at leastabout 0.05λ and/or not more than about 0.10λ, or not more than about0.075λ, wherein λ is the wavelength of the microwave energy introducedinto housing 1242 via first opening 1212. Adjacent plates 1244 a-d canbe spaced apart by a spacing distance, j, which can be greater than,approximately the same as, or less than the thickness of each plate. Inone embodiment, j can be at least about 0.01λ, at least about 0.05λand/or not more than about 0.10λ, or not more than about 0.075λ. Thus,in one embodiment, the ratio of the cumulative surface area of thedistal ends of plates 1244 a-d, generally illustrated as the shadedregions in FIG. 13c , to the total internal exposed surface area ofsecond end 1243 b of housing 1242, generally illustrated as the unshadedregions in FIG. 13c , can be at least about 0.85:1, at least about0.95:1, or at least about 0.98:1 and/or not more than about 1.15:1, notmore than about 1.10:1, or not more than about 1.05:1.

Variable phase short circuit 1230 can be configured to rotate at a speedof at least about 50 revolutions per minute (rpm), at least about 100rpm, at least about 150 rpm and/or not more than about 1000 rpm, notmore than about 900 rpm, or not more than about 800 rpm about axis ofrotation 1211, as illustrated in FIG. 13a . In one embodiment, at leasta portion of the movement of rotatable variable phase short circuit 1230can be carried out via an actuator 1270 coupled to an automatic driverand/or automatic control system (not shown). In another embodiment, atleast a portion of the movement can be carried out manually and mayoptionally include periods of non-rotation.

Additional embodiments of other rotatable phase shifting devices 1233and 1235 suitable for use in microwave distribution system 514 of FIG.6a , are illustrated in FIGS. 13e and 13f , respectively. As shown inthe embodiment depicted in FIG. 13e , rotating phase shifting device1233 can include a rotating crank member 1237 coupled via a securing rod1239 to a plunger 1241 disposed within a waveguide 1243. As crank member1237 rotates as indicated by arrow 1261, rod 1239 facilitates a generalup-and-down movement of piston or plunger 1241 within waveguide 1243, asindicated by arrow 1263 in FIG. 13e . Another embodiment of a rotatingphase shifting device 1235 is depicted in FIG. 13f as including a cam1245 coupled to a follower rod 1247, which can be integrated with orcoupled to a plunger 1241 disposed within waveguide 1243. As cam 1245rotates, follower rod 1247 moves plunger or piston 1241 in a generalup-and-down motion within cylinder 1243, as indicated generally by arrow1263. Additionally, according to one embodiment, rotating phase shiftingdevice 1235 can further comprise one or more biasing devices 1249 (e.g.,one or more springs) for facilitating movement of plunger 1241 withinwaveguide 1243 in an upward direction.

In addition to being utilized as a rotatable phase shifting device,variable phase short circuit 1230 (or, optionally, rotating phaseshifting devices 1233, 1235) can also be configured for use as a tuningdevice, such as, for example, as an impedance tuner for tuning out orcanceling unwanted reflections and/or as a frequency tuner for matchingthe frequency of the generator to that of the cavity.

Turning now to FIG. 14a , one embodiment of a microwave distributionsystem 1314 utilizing two variable phase short circuits 1330 a,b as animpedance tuner for canceling or minimizing reflected power isillustrated. As shown in FIG. 14a , each of variable phase shortcircuits 1330 a,b can be connected to adjacent outlets of a coupler1340, which can be a short slot hybrid coupler. In operation, each ofvariable phase short circuits 1330 a,b can be individually adjusted to adesired position such that impedance tuner tunes out energy reflectedfrom microwave launcher 1322 back toward generator 1312. According toone embodiment, one or both of variable phase short circuits 1330 a,bcan be further adjusted as needed during the microwave process in orderto accommodate changes in the reflection coefficient of the articlesbeing heated. In one embodiment, the further adjustments can be at leastpartially carried out using an automatic control system (not shown).

Variable phase short circuits as described herein can also be utilizedas frequency tuners for matching the frequency of the cavity to thefrequency of the generator. According to this embodiment, one or morevariable phase short circuits, shown as variable phase short circuit1330 c in FIG. 14b , can be directly coupled to individual ports spacedalong a resonant microwave chamber 1320. In this embodiment, variablephase short circuit 1330 c can be continuously or sporadically rotatedand its position can be manually or automatically adjusted depending onchanges within microwave chamber 1320 and/or the articles beingprocessed therein (not shown). As a result of this adjustment ofvariable phase short circuit 1330 c, the frequency of microwave energywithin the cavity can be more closely matched to the frequency of thegenerator (not shown).

Referring again to the microwave heating system 510 shown in FIG. 6a ,more thorough and/or more efficient heating of articles 550 passedthrough microwave chamber 520 may be carried out by, for example,increasing the heat transfer coefficient between the articles and thesurrounding fluid medium. One embodiment of a microwave chamber 1420configured to facilitate quicker and more efficient heating of articles1450 through changes in the heat transfer coefficient within microwaveheating chamber 1420 is illustrated in FIG. 15a . In one embodiment, theheat transfer coefficient within microwave chamber 1420 can beincreased, at least in part, by agitating the gaseous or liquid mediumwithin chamber 1420 using one or more agitation devices, such as, forexample, one or more fluid jet agitators 1430 a-d configured toturbulently discharge one or more fluid jets into the interior ofmicrowave chamber 1420. In one embodiment, the fluid jets dischargedinto microwave chamber 1420 can be a liquid or a vapor jet and can havea Reynolds number of at least about 4500, at least about 8000, or atleast about 10,000.

Structurally, fluid jet agitators 1430 a-d can be any device configuredto discharge a plurality of jets toward articles 1450 at multiplelocations within microwave chamber 1420. In one embodiment, fluid jetagitators 1430 can be axially spaced along the central axis ofelongation 1417 of microwave chamber 1420 such that at least a portionof the jets are configured to discharge in a direction generallyperpendicular to central axis of elongation 1417. In another embodiment,particularly shown in FIG. 15b , one or more fluid jet agitators 1430a-d can be circumferentially positioned within microwave chamber 1420such that at least a portion of the jets are directed radially inwardlytoward the central axis of elongation 1417 of chamber 1420. Althoughshown in FIG. 15b as being generally continuous along a portion of thecircumference of microwave chamber 1420, it should be understood thatfluid jet agitator 1430 a may also include a plurality of distinct jets,radially spaced from one another along at least a portion of thecircumference of chamber 1420, each positioned to discharge a fluid jettoward central axis of elongation 1417 of chamber 1420.

As shown in FIG. 15a , fluid jet agitators 1430 a-d can be positionedalong one or more sides of microwave chamber 1420 and can be disposedbetween (alternately) with one or more microwave launchers 1422. Use ofone or more agitators 1430 a-d can increase the heat transfercoefficient between the fluid medium within microwave chamber 1420 andarticles 1450 by at least about 1 percent, at least about 5 percent, atleast about 10 percent, or at least about 15 percent, as compared to theheat transfer coefficient of a quiescent chamber, ceteris paribus. Inthe same or another embodiment, one or more jets configured and/oroperated in a similar manner can be included within one or more otherzones of microwave system 10 including thermalization and/or holdingzones 12 and/or 20, illustrated previously in FIGS. 1a and 1 b.

Referring again to FIGS. 1a and 1b , after being withdrawn frommicrowave heating zone 16, the heated articles can then optionally berouted to a temperature holding zone 20, wherein the temperature of thearticles can be maintained at or above a certain minimum thresholdtemperature for a specified residence time. As a result of this holdingstep, the articles removed from holding zone 20 can have a moreconsistent heating profile and fewer cold spots. In one embodiment, theminimum threshold temperature within holding zone 20 can be the same asthe minimum temperature required within microwave heating zone 16 andcan be at least about 120° C., at least about 121° C., at least about122° C. and/or not more than about 130° C., not more than about 128° C.,or not more than about 126° C. The average residence time of articlespassing through holding zone 20 can be at least about 1 minute, at leastabout 2 minutes, or at least about 4 minutes and/or not more than about20 minutes, not more than about 16 minutes, or not more than about 10minutes. Holding zone 20 can be operated at the same pressure asmicrowave heating zone 16 and can, in one embodiment, be at leastpartially defined within a pressurized and/or liquid-filled chamber orvessel.

After exiting holding zone 20, the heated articles of microwave system10 can subsequently be introduced into a quench zone 22, wherein theheated articles can be quickly cooled via contact with one or morecooled fluids. In one embodiment, quench zone 22 can be configured tocool the articles by at least about 30° C., at least about 40° C., atleast about 50° C. and/or not more than about 100° C., not more thanabout 75° C., or not more than about 50° C. in a time period of at leastabout 1 minute, at least about 2 minutes, at least about 3 minutesand/or not more than about 10 minutes, not more than about 8 minutes, ornot more than about 6 minutes. Any suitable type of fluid can be used asa cooling fluid in quench zone 22, including, for example, a liquidmedium such as those described previously with respect to microwaveheating zone 16 and/or a gaseous medium.

According to one embodiment generally depicted in FIGS. 1a and 1b ,microwave heating system 10 may also include a second pressureadjustment zone 14 b disposed downstream of microwave heating zone 16and/or holding zone 20, when present. Second pressure adjustment zone 14b may be configured and operated in a manner similar to that previouslydescribed with respect to first pressure adjustment zone 14 a. Whenpresent, second pressure adjustment zone 14 b can be located downstreamof quench zone 22, such that a substantial portion or nearly all ofquench zone 22 is operated at an elevated (super atmospheric) pressuresimilar to the pressure under which microwave heating zone 16 and/orholding zone 20 are operated. In another embodiment, second pressureadjustment zone 14 b can be disposed within quench zone 22, such that aportion of quench zone 22 can be operated at a super-atmosphericpressure similar to the pressure of microwave heating zone 16 and/orholding zone 20, while another portion of quench zone 22 can be operatedat approximately atmospheric pressure. When removed from quench zone 22,the cooled articles can have a temperature of at least about 20° C., atleast about 25° C., at least about 30° C. and/or not more than about 70°C., not more than about 60° C., or not more than about 50° C. Onceremoved from quench zone 22, the cooled, treated articles can then beremoved from microwave heating zone 10 for subsequent storage or use.

In accordance with one embodiment of the present invention, one or moremethods for controlling the operation of microwave heating system 10 areprovided, for example, to ensure a consistent and continuous exposure tomicrowave energy for each article or package passing through microwaveheating system 10. The major steps of one embodiment of a method 1500suitable for controlling the operation of microwave system 10 aredepicted by individual blocks 1510-1530 in FIG. 16.

As shown in FIG. 16, the first step of control method 1500 is todetermine a value for one or more microwave system parameters related tomicrowave heating zone 16, as represented by block 1510. Examples ofmicrowave system parameters can include, but are not limited to, netpower discharged, speed of conveyance system, and temperature and/orflow rate of the water within the microwave heating chamber.Subsequently, as shown by block 1520 in FIG. 16, the resultingdetermined value for the specific parameter can then be compared to acorresponding target value for the same parameter in order to determinea difference. Based on the difference, one or more actions can be takento adjust the operation of microwave system 10, as represented by block1530 in FIG. 16. In one embodiment, the adjustment of microwave heatingsystem 10 can be undertaken when, for example, the magnitude of thedifference is at least about 5 percent, at least about 10 percent, or atleast about 20 percent of the value of the target value and/ordetermined value for the specific microwave system parameter. In oneembodiment, at least a portion of the above-described method can becarried out using an automatic control system.

In one embodiment, the basic steps of the above-described control method1500 can be utilized by microwave heating system 10 to ensure safetyand/or regulatory compliance of the articles (e.g., food and/or medicalfluids or equipment) being heated therein. According to this embodiment,the one or more microwave system parameters may be selected from thegroup consisting of minimum net power discharged, maximum speed ofconveyance system, and minimum temperature and/or minimum flow rate ofthe water within the microwave heating chamber. In one embodiment, theminimum temperature of the water in the microwave chamber can be atleast about 120° C., at least about 121° C., at least about 123° C.and/or not more than about 130° C., not more than about 128° C., or notmore than about 126° C., while the minimum flow rate can be at leastabout 1 gallon per minute (gpm), at least about 5 gpm, or at least about25 gpm. The maximum speed of the conveyance system, in one embodiment,can be not more than about 15 feet per second (fps), not more than about12 fps, or not more than about 10 fps and the minimum net powerdischarged can be at least about 50 kW, at least about 75 kW, or atleast about 100 kW. When control method 1500 is utilized to ensureproduct safety or compliance, the one or more actions taken to adjustthe operation of microwave heating system 10 can include, but are notlimited to, stopping the conveyance system, turning off one or moregenerators, removing, isolating, and re-running or disposing of one ormore articles exposed to undesirable conditions, and combinationsthereof.

In the same or another embodiment, the basic steps of control method1500 can also be utilized by microwave heating system 10 to ensurequality and consistency amongst the articles (e.g., food and/or medicalfluids or equipment) being heated. According to this embodiment, themicrowave parameters can include net power discharged, speed ofconveyance system, and temperature and/or flow rate of the water withinthe microwave heating chamber. In one embodiment, the temperature of thewater in the microwave chamber can be at least about 121° C., at leastabout 122° C., at least about 123° C. and/or not more than about 130°C., not more than about 128° C., or not more than about 126° C., whilethe flow rate can be at least about 15 gallons per minute (gpm), atleast about 30 gpm, or at least about 50 gpm. The speed of theconveyance system, in one embodiment, can be controlled to a speed of atleast about 5 feet per second (fps), at least about 7 fps, or at leastabout 10 fps, while the net power discharged can be at least about 75kW, at least about 100 kW, or at least about 150 kW. When control method1500 is utilized to ensure product quality or consistency, the one ormore actions taken to adjust the operation of microwave heating system10 can include, but are not limited to, stopping the conveyance system,turning off one or more generators, removing, isolating, and re-runningor disposing of one or more articles exposed to undesirable conditions,and combinations thereof.

In order to perform the comparison step 1520 of the method 1500 shown inFIG. 16, one or more of the target values for at least one of themicrowave system parameters discussed above can be determined prior toheating the articles in microwave system 10. Determination of themagnitude of these target values may be accomplished by first creating aprescribed heating profile for the specific type of article to be heatedusing a small-scale microwave system. For example, in one embodiment,one or more articles of a specific type (e.g., particular foodstuffs,medical devices, or medical fluids) are first be loaded into a microwavechamber of a small-scale microwave heating system. In one embodiment,the articles loaded into the small-scale heating chamber can be of asingle type such that the resultant prescribed heating determined can bespecifically applied to that type of article in a larger-scale heatingsystem. In one embodiment, the article can be a specific type and/orsize of packaged food (e.g., an 8-oz MRE package of meat) or can be apackaged medical fluid (e.g., saline) or specific types and/or packagesof medical or dental equipment.

Once loaded into the microwave chamber of the small-scale microwaveheating system, the article can be heated by introducing microwaveenergy into the chamber via one or more microwave launchers. During thisheating period, which can include multiple heating runs, a prescribedheating profile can be determined for the article being heated. As usedherein, the term “prescribed heating profile” refers to a set of targetvalues of a variety of parameters suggested or recommended for use whenheating a specific type of article. In addition to including a targetvalues, prescribed heating profiles can also be expressed, at least inpart, as a function of time and/or position of the article. In oneembodiment, the prescribed heating profile can include at least onetarget value for one or more microwave system parameters including, butnot limited to, net power discharged, sequential distribution ofmicrowave power (i.e., specifics regarding timing, location, and amountof microwave energy discharged), temperature and/or flow rate of thefluid (e.g., water) in the microwave chamber, and/or residence time ofthe article within the microwave chamber. In addition, the prescribedheating profile can also include target or minimum values for one ormore parameters (e.g., temperature, flow rate of fluid, pressure, andarticle residence time) related to thermalization, holding, and/orquench zones 16, 20, 22 of microwave heating system 10.

Once a prescribed heating profile has been determined, a plurality ofthat type of article can be loaded into a larger-scale microwave heatingsystem and can then be heated according to the prescribed profiledetermined with the small-scale microwave system, optionally with theuse of an automatic control system. In one embodiment, the small-scalemicrowave heating system can be a batch or semi-batch system and/or cancomprise a liquid-filled microwave chamber having a total internalvolume of less than 100 cubic feet, less than 50 cubic feet, or lessthan 30 cubic feet. In the same or another embodiment, the large-scalemicrowave system can be a continuous or semi-continuous process at leastpartially carried out in a pressurized or liquid filled microwavechamber having a total internal volume of at least about 100 cubic feet,at least about 250 cubic feet, or at least about 500 cubic feet. Theabove-described steps can subsequently be repeated as many times asneeded in order to create specific prescribed heating profiles for anynumber of different articles. Subsequently, target values for one ormore parameters described above can be determined and used in thecomparison step 1520 of method 1500 shown in FIG. 16. Thereafter andbased on the difference, one or more of the actions listed above may betaken to ensure consistent heating of the final product.

One aspect of ensuring consistent heating is ensuring constant andmeasurable power discharged into the heating zone. In one embodiment, amethod for controlling the net power discharged within microwave heatingsystem 10 is provided. As used herein, the term “net power discharged”refers to the difference between the forward and reflected power withina waveguide or launcher. As used herein, the term “forward power” refersto power propagating in an intended direction from the generator to aload, while the term “reflected power” refers to power propagating in anon-intended direction, usually from the load back into a waveguide orlauncher and toward the generator.

The major steps of a method 1600 for determining the net powerdischarged from at least one microwave launcher using two or more pairsof directional couplers are summarized in the flow chart provided inFIG. 17. As represented by blocks 1610 and 1620, a first and secondvalue for net power discharged can be determined using two independentpairs of directional couplers. Each pair of directional couplers caninclude one coupler for measuring forward power and another formeasuring reflected power and one or more devices or systems forcalculating the difference to thereby provide respective first andsecond values for net power discharged. According to one embodiment, atleast one of the net power values can be used to adjust or control theoutput of the microwave generator, while the other can be used as abackup or validation of the other.

Once values have been obtained from each pair of couplers, the first andsecond values for net power can be compared to determine a difference,as illustrated by block 1630, and, based on the difference, an actioncan be taken to adjust the operation of the microwave heating system, asdepicted by block 1640. In one embodiment, the action can be taken whenthe difference exceeds a predetermined value, such as, for example, avalue that is at least about 1 percent, at least about 2 percent, or atleast about 5 percent of the first and/or second net power valuesdetermined previously. In one embodiment, action can be taken when thedifference is at least about 1 percent, at least about 2 percent, or atleast about 3 percent of the lowest of first and second net powervalues. In another embodiment, action may also be taken if one of firstor second net power values falls below a predetermined minimum and/orexceeds a predetermined maximum. Depending, at least in part, on thearticles being processed and the difference determined, the action mayinclude, but is not limited to, shutting down a generator or conveyancesystem, increasing or decreasing generator output, and/or removing,isolating, and disposing or re-running one or more articles that weredisposed within the microwave heating chamber when the differenceexceeded the predetermined value.

Microwave heating systems of the present invention can becommercial-scale heating systems capable of processing a large volume ofarticles in a relatively short time. In contrast to conventional retortsand other small-scale systems that utilize microwave energy to heat aplurality of articles, microwave heating systems as described herein canbe configured to achieve an overall production rate of at least about 15packages per minute per convey line, at least about 20 packages perminute per convey line, at least about 25 packages per minute per conveyline, or at least about 30 packages per minute per convey line, whichfar exceeds rates achievable by other microwave systems.

As used herein, the term “packages per minute” refers to the totalnumber of whey gel-filled 8-oz MRE (meals ready to eat) packages able tobe processed by a given microwave heating system, according to thefollowing procedure: An 8-oz MRE package filled with whey gel puddingcommercially available from Ameriqual Group LLC (Evansville, Ind., USA)is connected to a plurality of temperature probes positioned in thepudding at five equidistant locations spaced along each of the x-, y-,and z-axes, originating from the geometrical center of the package, asshown in FIG. 18. The package is then placed in a microwave heatingsystem being evaluated and is heated until each of the probes registersa temperature above a specified minimum temperature (e.g., 120° C. forsterilization systems). The time required to achieve such a temperatureprofile, as well as physical and dimensional information about theheating system, can then be used to calculate an overall production ratein packages per minute.

The preferred forms of the invention described above are to be used asillustration only, and should not be used in a limiting sense tointerpret the scope of the present invention. Obvious modifications tothe exemplary one embodiment, set forth above, could be readily made bythose skilled in the art without departing from the spirit of thepresent invention.

The inventors hereby state their intent to rely on the Doctrine ofEquivalents to determine and assess the reasonably fair scope of thepresent invention as pertains to any apparatus not materially departingfrom but outside the literal scope of the invention as set forth in thefollowing claims.

The invention claimed is:
 1. A continuous process for heating aplurality of articles in a microwave heating system, said processcomprising: (a) securing said plurality of articles in a plurality ofindividual carriers; (b) thermalizing said articles in said carriers ina thermalization zone to thereby provide a plurality of thermalizedarticles having a substantially uniform temperature; (c) before or aftersaid thermalizing of step (b), passing said plurality of articles insaid carriers through a pressure adjustment zone in a discontinuousfashion to increase the pressure around said articles to an elevatedpressure that is at least 5 psig; (d) heating said thermalized articlesin said carriers in a microwave heating zone maintained at or above saidelevated pressure to thereby increase the average temperature of eacharticle by at least 50° C., wherein at least a portion of said heatingis carried out at a heating rate of at least 25° C. per minute, whereinsaid articles are submerged in a liquid medium during said heating ofstep (d); and (e) cooling the heated articles in said carriers in aquench zone, wherein said articles are passed through each of saidthermalization zone, said microwave heating zone, and said quench zonevia one or more conveyance systems, wherein said microwave heatingsystem has an overall production rate of at least 20 packages per minuteper convey line.
 2. The process of claim 1, wherein said thermalizationzone is at least partially filled with said liquid medium.
 3. Theprocess of claim 1, wherein said heating of step (d) includesdischarging microwave energy into said microwave chamber via at leastone pair of opposed launchers disposed on generally opposite sides ofsaid microwave chamber.
 4. The process of claim 3, wherein said opposedlaunchers are staggered relative to one another along the central axisof elongation of said microwave chamber.
 5. The process of claim 3,wherein said opposed launchers are oppositely facing launchers.
 6. Theprocess of claim 1, wherein at least a portion of said heating of step(d) is carried out under a pressure of at least 10 psig.
 7. The processof claim 1, wherein said microwave heating zone comprises a microwavechamber at least partially filled with said liquid medium, wherein atleast a portion of said heating of step (d) is carried out at atemperature above the normal boiling point of said liquid medium.
 8. Theprocess of claim 1, wherein at least a portion of said thermalizing ofstep (b) is carried out at a different pressure than said heating ofstep (d), further comprising, subsequent to said thermalizing of step(b), passing said articles through said pressure adjustment zone.
 9. Theprocess of claim 1, wherein said substantially uniform temperature ofsaid articles exiting said thermalization zone is at least 20° C. andnot more than 70° C.
 10. The process of claim 1, wherein said articleshave an average residence time in said thermalization zone of at least 2minutes and not more than 20 minutes.
 11. The process of claim 1,wherein the residence time of said articles in said microwave chamber isat least 30 seconds and not more than 10 minutes.
 12. The process ofclaim 1, further comprising prior to said cooling of step (e), passingsaid heated articles through a holding zone, wherein the temperature ofsaid articles is maintained at or above a specified minimum temperaturefor a time period of at least 2 minutes and not more than 15 minutes insaid holding zone.
 13. The process of claim 12, wherein said specifiedminimum temperature is at least 120° C. and wherein said holding zonecomprises a liquid-filled chamber operated at a pressure of at least 10psig.
 14. The process of claim 1, wherein said microwave heating systemis a pressurized microwave system and pasteurizes or sterilizes saidarticles.
 15. The process of claim 14, wherein said articles comprisepackages containing foodstuffs, medical fluids, or medical instruments.